The Holy Roman Empire is a different institution than the Roman Empire; it had an official with the title "emporer" but it also featured rather extreme decentralization of power. And it existed at the same time as the early US. In some respects, it was the direct model for the decentralization in the US system.

Also, "no central bank" wasn't domething that made the US decentralized compared to other contemporary systems. First, because central banks were extremely rare at the time, and second because the central banks of the time, and most modern ones, are a means of transferring power out of the government to private capitalists, so they further decentralize government power.

Neither was retaining the British jury system.